Harvest is upon us and another irrigation season – such as it was in our neck of the woods – is over, so a recap of the recently concluded water year from Central’s perspective is in order. (Note: A “water year” runs from Oct. 1 to Sept. 30 of the following year.)
It was somewhat of an unusual summer, at least in south-central Nebraska. Conditions and experiences in other parts of Nebraska, being a state of much variability, may have differed considerably. But by most accounts, irrigation demand was relatively low this summer, whether the water was delivered from a canal system or pumped from a well.
The post-season data shows that deliveries from Central’s system were well below normal. That’s probably a good thing because, after three consecutive years in which inflows to Lake McConaughy exceeded 1 million acre-feet (a-f), the 2017-18 water year failed to reach that level, amounting to just under 900,000 a-f. This comes on the heels of two consecutive years of below average snowmelt runoff that feeds the North Platte River.
Under different circumstances this might be cause for concern about the reservoir’s storage conditions, but not so much this year. While there are many factors in play, reduced irrigation demand across much of the Platte Valley helped keep water in Lake McConaughy.
As a reminder to readers, water from Lake McConaughy is released not only for Central’s irrigation customers, but for diversion by many other canals in the Platte Valley.
At first glance, reduced irrigation demand could be attributed to abundant rainfall and temperatures that, by and large, stayed below scorching levels. While temperatures rarely climbed above the low 90s, precipitation – at least in Central’s area – didn’t depart that much from normal this summer, although seldom a week went by without some precipitation. Perhaps more so than the amount, the timeliness and effectiveness of rainfall helped reduce irrigation demand.
Rain gauges in the area accumulated various amounts of precipitation during the growing season (April-September), with average for that period in parentheses: 21.81” north of Elwood (17.28”); 23.26” in the Bertrand area (17.55”); 20.14” inches north of Holdrege (20.36”); and 17.67” inches north of Minden 19.81”). Keep in mind that these totals include rainfall in September – which was fairly wet — when crop water use was low.
While it might have seemed wet, we didn’t see a dramatic departure from the norm this year.
Lake McConaughy reached its peak elevation on June 11 at 3257.0 feet above mean sea level. It’s low elevation for the year was reached on Sept. 9 at 3252.4 feet. That decline – 4.6 feet – is among the lowest irrigation-season declines on record.
While that small of a decline is unusual – the reservoir typically drops between 10 and 15 feet during a “normal” irrigation season – there have been summers when the lake actually gained elevation due to a variety of factors (high inflows, plentiful rainfall, high South Platte River flows which reduced the need for releases from Lake McConaughy, and the summer of ’93 when widespread hail storms and late crop freezes and 40 inches of rain significantly impacted demand for irrigation water in south-central Nebraska).
In fact, perusal of the data revealed that Lake McConaughy gained elevation during irrigation season on seven occasions: 1947, 1962, 1965, 1993, 1999, 2010 and 2015. And in 1958 the lake was at the same elevation at the end of September as it was on the first of May.
In summary, Lake McConaughy weathered the summer of 2018 quite well and storage conditions are good. Upstream reservoirs in Wyoming are also in fairly good shape entering the fall and winter. But it sure would be nice to see some snowfall on those mountains by next April.